Re: Syscall from Kernel Space

[Andrea Arcangeli <andrea@suse.de>]

On Thu, Feb 20, 2003 at 05:17:30PM -0500, Jeff Garzik wrote:
> On Thu, Feb 20, 2003 at 11:10:27PM +0100, Andrea Arcangeli wrote:
> > On Thu, Feb 20, 2003 at 12:40:43PM -0500, Jeff Garzik wrote:
> > > On Thu, Feb 20, 2003 at 11:04:37PM +0530, Prasad wrote:
> > > > 	Is there a way using which i could invoke a syscall in the kernel 
> > > > space?  The syscall is to be run disguised as another process.  The actual 
> > > 
> > > Call sys_<syscall>.  Look at the kernel code for examples.
> > > 
> > > Note that typically you don't want to do this... and you _really_ don't
> > > want to do this if the syscall is not one of the common file I/O
> > > syscalls (read/write/open/close, etc.)
> > 
> > you never want to do this, the only point of a syscall is to enter
> > kernel, if you're just in kernel you're wasting time in calling the
> > syscall (not to tell about the new non soft interrupt based syscall
> > instructions, btw this is also why I rejected the int 0x81 thing on
> > x86-64 for 64bit syscalls)
> 
> He is talking about directly calling the function behind the syscall,
> not actually executing a syscall itself.

this is not what I understood from your previous discussion also given
you suggest not to do that when he can call sys_read/sys_write instead
because they're just exported etc.. I just wanted to add a better
"never".

> syscalls should be made from userspace, not the kernel.

This is what I tried to say.

Andrea